HCI in the software process

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chapter 6

• HCI in the software process

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HCI in the software process

• Software engineering and the design process for
  interactive systems
• Usability engineering
• Iterative design and prototyping
• Design rationale

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the software lifecycle

• Software engineering is the discipline for
  understanding the software design process, or
  life cycle
• Designing for usability occurs at all stages of
  the life cycle, not as a single isolated activity

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The waterfall model
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Activities in the life cycle

• Requirements specification
• designer and customer try capture what the system
  is expected to provide can be expressed in
  natural language or more precise languages, such
  as a task analysis would provide
• Architectural design
• high-level description of how the system will
  provide the services required factor system into
  major components of the system and how they are
  interrelated needs to satisfy both functional and
  nonfunctional requirements
• Detailed design
• refinement of architectural components and
  interrelations to identify modules to be
  implemented separately the refinement is governed
  by the nonfunctional requirements

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Verification and validation

• Verification
• designing the product right
•  Validation
• designing the right product
•  
• The formality gap
• validation will always rely to some extent on
  subjective means of proof
• Management and contractual issues
• design in commercial and legal contexts

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The life cycle for interactive systems

• cannot assume a linearsequence of activitiesas
  in the waterfall model
• lots of feedback!

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Usability engineering

• The ultimate test of usability based on
  measurement of user experience
• Usability engineering demands that specific
  usability measures be made explicit as
  requirements
• Usability specification
• usability attribute/principle
• measuring concept
• measuring method
• now level/ worst case/ planned level/ best case
• Problems
• usability specification requires level of detail
  that may not be
• possible early in design satisfying a usability
  specification
• does not necessarily satisfy usability

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part of a usability specification for a VCR

• Attribute Backward recoverability
• Measuring concept Undo an erroneous programming
  sequence
• Measuring method Number of explicit user
  actions to undo current program
• Now level No current product allows such an undo
• Worst case As many actions as it takes to
  program-in mistake
• Planned level A maximum of two explicit user
  actions
• Best case One explicit cancel action

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ISO usability standard 9241

• adopts traditional usability categories
• effectiveness
• can you achieve what you want to?
• efficiency
• can you do it without wasting effort?
• satisfaction
• do you enjoy the process?

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some metrics from ISO 9241

• Usability Effectiveness Efficiency
  Satisfactionobjective measures
  measures measures
• Suitability Percentage of Time to Rating scale
  for the task goals achieved complete a
  task for satisfaction
• Appropriate for Number of power Relative
  efficiency Rating scale fortrained
  users features used compared with satisfaction
  with an expert user power features
• Learnability Percentage of Time to learn Rating
  scale for functions learned criterion ease of
  learning
• Error tolerance Percentage of Time spent on
  Rating scale for errors corrected correcting
  errors error handling successfully

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Iterative design and prototyping

• Iterative design overcomes inherent problems of
  incomplete requirements
• Prototypes
• simulate or animate some features of intended
  system
• different types of prototypes
• throw-away
• incremental
• evolutionary
• Management issues
• time
• planning
• non-functional features
• contracts

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Techniques for prototyping

• Storyboards
• need not be computer-based
• can be animated
• Limited functionality simulations
• some part of system functionality provided by
  designers
• tools like HyperCard are common for these
• Wizard of Oz technique
• Warning about iterative design
• design inertia early bad decisions stay bad
• diagnosing real usability problems in
  prototypes.
• . and not just the symptoms

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Design rationale

• Design rationale is information that explains why
  a computer system is the way it is.
• Benefits of design rationale
• communication throughout life cycle
• reuse of design knowledge across products
• enforces design discipline
• presents arguments for design trade-offs
• organizes potentially large design space
• capturing contextual information

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Design rationale (contd)

• Types of DR
• Process-oriented
• preserves order of deliberation and
  decision-making
• Structure-oriented
• emphasizes post hoc structuring of considered
  design alternatives
• Two examples
• Issue-based information system (IBIS)
• Design space analysis

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Issue-based information system (IBIS)

• basis for much of design rationale research
• process-oriented
• main elements
• issues
• hierarchical structure with one root issue
• positions
• potential resolutions of an issue
• arguments
• modify the relationship between positions and
  issues
• gIBIS is a graphical version

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structure of gIBIS
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Design space analysis

• structure-oriented
• QOC hierarchical structure
• questions (and sub-questions)
• represent major issues of a design
• options
• provide alternative solutions to the question
• criteria
• the means to assess the options in order to
  make a choice
• DRL similar to QOC with a larger language and
  more formal semantics

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the QOC notation
Criterion
Option
Question
Option
Criterion
Option
Criterion
ConsequentQuestion


Question
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Psychological design rationale

• to support task-artefact cycle in which user
  tasks are affected by the systems they use
• aims to make explicit consequences of design for
  users
• designers identify tasks system will support
• scenarios are suggested to test task
• users are observed on system
• psychological claims of system made explicit
• negative aspects of design can be used to improve
  next iteration of design

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Summary

• The software engineering life cycle
• distinct activities and the consequences for
  interactive system design
• Usability engineering
• making usability measurements explicit as
  requirements
• Iterative design and prototyping
• limited functionality simulations and animations
• Design rationale
• recording design knowledge
• process vs. structure